A wide variety of articles are manufactured by casting various metals, e.g. cast iron, aluminum, brass, magnesium, bronze, etc., such as engine blocks, engine heads, valve bodies, pipe fittings, carburetor bodies and the like. With any of the metal casting processes in general use, it is typical for a minor proportion of the articles to have pores that extend through or partially through a wall of the casting. Because these pores can impair the usefulness of the cast article, such as by resulting in gaseous or fluid leakage, the art of impregnating castings to fill the pores has developed in order that the castings can be made suitable for their intended use instead of being scrapped.
A commonly practiced technology for impregnation of metal castings includes the steps of submerging the castings in a bath of liquid sealant in an enclosed impregnation tank, and then evacuating the tank to a sufficiently low vacuum to enable air entrapped in any pores in the castings to escape so that the pores can be filled with liquid sealant. The vacuum in the impregnating tank is then released and the castings are transferred to a tank in which the excess sealant is allowed to drain off. The castings are transferred to another tank in which they are rinsed with water and/or detergent in order to wash off excess sealant. Next, the castings are transferred to a curing vessel to allow the sealant to cure to a solid material to fill the pores in a casting, which generally involves a thermal curing with the use of heated oil or water.
Many types of thermosetting resin compositions are used as liquid sealants for vacuum impregnation of metal castings. Unsaturated polyesters, often incorporating low viscosity monomers such as styrene inhibitors and catalysts, may be employed. Sodium silicate sealant compositions are also used. Other thermosetting liquid sealant compositions include monofunctional and polyfunctional acrylate monomers, generally mixed with a catalyst and inhibitor. The sealant may be curable under anaerobic conditions or oxygen-containing conditions. Representative patents disclosing liquid sealant compositions include British Pat. Nos. 1,297,103 and 1,308,947, and U.S. Pat. Nos. 2,554,254, 2,932,583, 3,345,205, 4,069,378 and 4,147,821.
A major impregnation technique practiced at this time is the "wet vacuum" process in which a casting is first submerged in liquid sealant in an impregnation tank, and thereafter a suitable vacuum is developed in the tank. There have been proposals to employ a "dry vacuum" impregnation step in which the castings are placed in a closed impregnation tank and subjected to a vacuum, after which liquid sealant is transferred from a reservoir into the tank for filling the pores in the castings. See for example, U.S. Pat. Nos. 2,932,583, 3,345,205 and 4,311,735. Equipment for single tank dry vacuum impregnation of sintered articles was sold for a time by American Metaseal. However, no commercial use of single tank dry vacuum impregnation for metal castings is known to the present inventor as of the filing date hereof, and it is believed this is due to the unavailability of equipment suitable for its practice.
My present invention relates to a dry vacuum single tank metal casting impregnation system. The principal objectives of the development of this invention were: the provision of a dry vacuum impregnation system which is believed to be practical for commercial use; the development of an impregnation apparatus that will enable efficient practice of dry vacuum impregnation of metal castings; the provision of an impregnation apparatus that will offer economies as to capital investment and operating costs; the provision of an impregnation system suitable for in-line arrangement of the several required pieces of equipment; the provision of an impregnation apparatus which can be readily combined with material handling equipment; considerable reduction of the time required for the actual impregnation process; and provision for spin-off of excess resin from the castings while in the impregnation apparatus.